Safety device for transformers with expansion tanks



May 1 9, 1 953 L. J. EGGER 2,639,308

SAFETY DEVICE FOR TRANSFORMERS WITH EXPANSION TANKS Filed July 18, 1949 E www HTM/@NE Yi Patented May 19, 1953 SAFETY DEVICE FOR TRANSFORMERS WITH EXPANSION TANKS Lon Jean Egger, Aix-les-Bains, France, assignor to Societe Savoisienne de Constructions Electriques, Aix-les-Bains, France, a French corporation i, Application July 18, 1949, Serial No. 105,431

In France July 20, 1948 8 Claims.

. l g This invention relates to safety devices and is more particularly concerned with safety devices for use on electrical apparatus such as trans formers.

Modern transformers provided with safety devices are generally equipped with float relays or switches of the Buchholz type or the like such as are described in the Buchholz Patent No. 1,642,- 398. Such float relays break the circuit or give an alarm in the event of the evolution of gases due to a more or less serious fault within the container of the transformer. Usually the float relay is located in a pipe extending from the highest point of the container and opening in the bottom or at Aleast a few centimetres from the bottom of the oil reservoir. This arrangement has a number of disadvantages:

During norma1 operation, the breathing of the transformer takes place through the relay pipe. Consequently, upon heating, it is the hot, and hence oxidizable, oil from the top of the container which rises into the reservoir and becomes oxidized in contact with the air. Consequently, upon cooling, the oil at the bottom of the reservoir, which is charged with the products of oxidation flows towards the container and is deposited on the'top of the windings. This deposition of impurities reduces the emciency of the insulation.

The tripping of the circuit breaker or the alarm signal by the yfloat relay does not occur until a considerable amount of gas is evolved. In fact, the float relay is so adjusted that it is insensitive to movements due to contraction or expansion of the oil. If an external accident results in breakage of a terminal or renting of the tank, the circuit breaker is not tripped until all the oil has drained away from the reservoir. In addition to the belated operation of the relay, the oil in the reservoir is then entirely lost and may feed any nre which breaks out at the point at which the oil escapes.

Finally in the case of a violent explosion inside the container, the transformer is immediately placed out of circuit, but the small cross section of the float relay pipe is not sufficient to allow the oil to expand and a second pipe comprising an explosion funnel must be provided.

Similar protective devices are also known which comprise, in addition to the means hereinbefore referred to a partially or completely closing non-return valve situated between the float relay and the reservoir. .c

o In such latter cases, the float relay is sensitive tothe refluxl movements ofw thev oil towards the 2 container and electrically controls the closing of the non-return valve. In this Way, the draining away of the oil in the case of such reflux is partially or completely avoided, but all the other disadvantages hereinbefore referred to remain, and the operation of the non-return valve is dependent upon the correct energization of an electric circuit which may be damaged before the valve should come into operation. 4

The object of the present invention is to provide a protective device for transformers, by means of which' these disadvantages can. be

overcome. Y

According to the present invention there is provided a safety device for use on electrical apparatus of a type having a part or parts thereof immersed in oil in a container, there being used with the container a reservoir containing a reserve of oil associated therewith, and a nonreturn valve inserted in a pipe connecting the container to the reservoir, said pipe entering said container below the oil level therein and the non-return valve being adjusted so that the oil in the container can expand and contract normally without affecting the non-return valve, while oil cannot flow from the reservoir to the container in large amounts, and further comprising a gas detecting device inserted in another pipe connecting the container to its reservoir, the said other pipe entering into both containers above the oil levels therein, said gas detecting device being such as a float relay having a chain-` ber which collects the gas formed in the container and Will cause operation of electric contacts by a float after the gas collected reaches a predetermined volume in order to ring a bell or break an electrical circuit when brought into operation. The float relay is brought into operation when the transformer is not operating properly or has been damaged as by having its terminals broken, or the oil has fermented or decomposed, by virtue of such improper operation or damage, causing the formation of gas within the container A which holds the transformer. This improper operation or damage causes a marked temperature rise or the formation of electric arcs, which produces boiling or decomposition of the oil, and the formation of the mentioned gas. This gas so formed rises in the container A from which it passes after being collected into the chamber of the float relay. The presence of bubbles of gas in this chamber of the ioat relay causes a decrease in the specific gravity of the oil, the float falls, and actuates a circuit control surges from said casing to saidreservoir and to block surges from said reservoir to said casing.

8. Apparatus, according to claim 4, and a nonreturn Valve inserted in saidpsecond pipe and remaining unactuated by normal oil expansion and contraction but being actuatable to pass explosive surges from said casing to said reservoir and to block surges from said reservoir to said casing, and said second pipev extending to the outside of the upper part of said reservoir.

LON JEAN EGGER.

References Cited in the le of this patent UNITED STATES PATENTS Name Date Moody Aug. 4, 1925 Buchholz Sept. 13, 1927 Buchholz Sept. 13, 1927 Moody Oct. 23, 1928 Troy Sept. 17, 1940 

